DE10232757B4 - Apparatus and method for humidifying a gas flow - Google Patents

Abstract

contraption for moistening at least one to a fuel cell system flowing gas stream, this gas stream flows through a humidifier which also a moist gas stream, especially a humid Exhaust gas stream from the fuel cell system, flows, and wherein the two gas streams through one or more for Water vapor permeable Membrane (s) are separated from each other, characterized in that at least one bypass line (12, 13) is provided, through which at least one of the gas streams partly so led is that he does not come into contact with the membrane (8).

Description

The The invention relates to a device for moistening at least one to a fuel cell system flowing gas stream, after the in the preamble of claim 1 closer defined type.

in principle The prior art knows two different types of PEM fuel cell systems (PEM = polymer electrolyte membrane). One distinguishes between fuel cell systems with one Gas generating device and those which directly with hydrogen operate. In fuel cell systems with gas generating device In the gas generating device, a hydrogen-containing gas generated for operating the fuel cell. In general, this will a hydrocarbon-containing compound, for example alcohol, Gasoline or diesel, together with water and possibly air converted into a hydrogen-rich gas and carbon dioxide.

at Both fuel cell systems described above must the the Cathode area of the PEM fuel cell supplied air, or another oxygenated medium, to be moistened according to the Preserve PEM from dehydration. In addition, in fuel cell systems with a gas generating device, the water balance of the fuel cell system if possible to be self-contained, on the one hand the moistening of the PEM ensure and on the other hand without constant refueling enough water for the To provide operation of the gas generating device. The water serves, especially in liquid Saved form, then for a hot steam reforming or autothermal reforming of the Hydrogen recovery used hydrocarbon containing compound in the gas generating facility.

In the PEM fuel cell itself is an anode compartment, which the Hydrogen or the hydrogen-containing gas is supplied, through the PEM, which is usually as part of a membrane electrode assembly (MEA - Membrane Electrode Assembly) is separated from the cathode compartment, which is an oxygenated Medium, especially air, fed becomes. In the fuel cell is at the currently usual Build up at the same time water from the anode side to the cathode side of the PEM transports. Likewise arises in the implementation of hydrogen and oxygen the product water. This product water is usually by removed an exhaust stream from the cathode compartment.

The US 6,007,931 as well as the US 6,048,383 now describe corresponding methods in which the moist exhaust gas flow from the cathode space is passed through a humidifier, which has a membrane permeable to water vapor. The water vapor contained in the exhaust gas stream can thus pass through the membrane and moisten a gas stream flowing in the humidifier on the other side of the membrane. This gas stream may in particular be the air supplied in the cathode chamber.

at This method is now in the inflowing the cathode compartment, to be humidified gas flow a dew point, which is substantially from the temperature of the cathode exhaust gas, the transmission capacity of the membrane and the load point of the fuel cell system. It can it with higher transmission power However, come to that in the humidified, the cathode compartment supplied Gas flow set such high dew points that reliable operation the fuel cell is no longer guaranteed. Instead of one meaningful moistening, there is practically a "flooding" of the PEM or the arranged in their area electrons / catalysts and / or of the cathode compartment, the electric power of the fuel cell falls with it from.

It Therefore, the object of the present invention, a simple and compact to perform Apparatus and method for moistening at least one flowing a fuel cell system Gas stream, where there is a possibility of the dew point in the at least one to be humidified gas stream to vary and in particular set to a respective predetermined value.

According to the invention this Task by the mentioned in the characterizing part of claim 1 Characteristics solved.

One Method of solution the above object in combination with the device according to claim 1 results from the characterizing part of claim 14.

Especially favorable Uses for the above-mentioned device according to the invention and optionally the above-mentioned inventive method arise from the claims 15 or 16.

By the at least one bypass line can be in a particularly simple and effectively the volume flow on at least one side the for Permeable to water vapor Affect membrane.

Thus, the volume flow, which is to be moistened and absorbs the steam, can be varied. This can then eg with be mixed with the passing through the bypass line part, which can be set in the mixture of the desired dew point. A variation of the dew point is thus possible by a simple device, for example by means of proportional valves or the like.

alternative This can also be a part of the moist gas through a bypass line around the membrane become. By doing so leaves about one also very simple influencing of the volume flows, e.g. by a valve means, the amount of water vapor offered change, which also the humidification of the gas stream to be humidified vary leaves. Even so lets with very simple means the dew point in the humidified and later e.g. influence a gas stream fed to a fuel cell.

According to one especially favorable Further development of the above invention is the moist exhaust gas flow after flowing through the humidifier and / or the bypass line in another similarly designed humidifier for humidifying a led further gas stream. In This construction ensures that the whole in the exhaust stream present moisture or the water vapor recovered and the system for disposal is provided. This affects, for example, a fuel cell system particularly positive on its water balance, so here on a Refueling of water to operate the fuel cell system can be waived.

According to one other very cheap Embodiment of the invention is the at least one bypass line integrated into the humidifier itself.

Thereby creates a very compact and space-saving construction, which in particular when using the invention in a fuel cell system in a motor vehicle, boat or the like of particular advantage is.

In a development of the invention, the device according to the invention can be also for drying a gas stream use.

That's just an inverse of "useful gas flow" and "exhaust gas (stripping gas) flow necessary. So a humid gas stream can over a first dry and after the humidifier then wet stripping gas flow in a precisely adjustable ratio be dehumidified.

Further advantageous embodiments of the invention will become apparent from the remaining dependent claims and will be described with reference to the embodiment described below explained in more detail with reference to the drawings.

there demonstrate:

1 a fuel cell system in an embodiment according to the invention;

2 a possible construction of a humidifier according to the invention in a schematic representation;

3 a structure of the humidifier according to 2 with a device for varying the volume flow through a bypass line;

4 Another possible structure of a device for varying the volume flow through the bypass line;

5 a further alternative construction of a device for varying the volume flow through the bypass line;

6 Another possible construction of a humidifier according to the invention in a schematic representation;

7 an alternative embodiment of the fuel cell system according to the invention; and

8th a further alternative embodiment of the fuel cell system according to the invention.

following the invention is based on a device for moistening a Gas stream for a fuel cell system described in detail, it should be so but not limited to this specific application.

In 1 is a fuel cell system 1 shown. The fuel cell system 1 has at least one fuel cell 2 which can be constructed as a single cell or, in particular, as a fuel cell stack consisting of a plurality of individual cells. The fuel cell 2 has a proton-conducting membrane 3 , in particular a PEM, on which an anode space 4 from a cathode compartment 5 the fuel cell 2 separates. In the fuel cell 2 is now from a hydrogenous medium, which is the anode compartment 4 is fed and an oxygen-containing medium, which is the cathode compartment 5 is supplied, electrical power generated in a conventional manner. Neither this electric power nor the manner in which the hydrogen-containing medium is generated and / or supplied plays a role for the moistening devices shown here.

An example is the one shown here The fuel cell system 1 an optional gas generating device 6 indicated in which of a compound having carbon and hydrogen together with water and optionally an oxygen-containing medium, a hydrogen-rich gas is generated. However, the operation of the invention is in principle also in other fuel cell systems 1 For example, those which are supplied in a tank stored hydrogen gas, possible.

In the fuel cell system shown here 1 That's the fuel cell 2 produced product water, usually in the region of the cathode space 5 , attack. This product water is then removed from the cathode compartment together with an exhaust gas stream 5 dissipated. At the same time, the cathode compartment is needed 5 in the supply of the oxygen-containing medium, in particular air, but also a defined moisture content or dew point to dehydration of the membrane, for example, constructed as a polymer electrolyte membrane 3 to prevent.

The exhaust stream from the cathode compartment 5 will therefore be in a humidifier 7 directed. In this humidifier 7 there is at least one membrane 8th which is impermeable to the exhaust gas per se and permeable to the water vapor contained in the exhaust gas. Such membranes 8th are known in the art and may consist of various polymeric materials, hollow fiber membranes or the like. On the other side of the membrane 8th flows to be moistened gas stream, which flows through the membrane 8th reaching water vapor and then in the embodiment shown here the cathode compartment 5 is supplied as humidified supply air. To promote this gas flow is located in front of the humidifier 7 a corresponding conveyor 9 , eg a compressor. The exhaust stream is, before leaving the area of the cathode compartment 5 in the humidifier 7 passes, by means of a heat exchanger 10 cooled, so that a part of the product water can condense out. This condensed and another, of the exhaust gas flow liquid entrained part of the product water of the fuel cell is between the heat exchanger 10 and the humidifier 7 in a liquid separator 11 liquid deposited. This liquid separated water can then be used for other purposes, which will be discussed in more detail in the embodiments still shown below.

In such a fuel cell system 1 is thus ensured in a simple and effective manner that at least the at least approximately the largest part of the water located in the exhaust gas stream is recovered. In particular, part of the water vapor present in the exhaust gas stream becomes the necessary moistening of a gas stream, in particular the supply air to the cathode chamber 5 used. It is disadvantageous that the transmission of the water vapor and thus the humidification of the gas stream to be humidified by the size of the membrane 8th is fixed. However, in order to be able to realize here a desirable setting of the dew point in the humidified gas flow, which is necessary in certain load conditions, in order to ensure an excessively high water content around the area of the cathode space 5 to prevent this because the performance of the fuel cell 2 would be detrimental.

To influence the dew point of the gas stream to be humidified sees the fuel cell system shown here 1 Now at least one of two, shown here by dashed lines, bypass lines 12 . 13 , in front. In principle, each of the two bypass lines 12 . 13 alone able to realize an adjustment of the dew point in the gas stream to be humidified with the simplest means. Next to each one of the bypass lines 12 . 13 In addition, a combination, ie the presence of two bypass lines 12 and 13 in the fuel cell system 1 , be provided. The operation of the bypass lines will be explained in detail below.

The bypass line 12 , Which has a device, not shown here, for varying the volume flow flowing into it, through which the proportion of the volume flow of the exhaust gas flowing through the bypass line 12 flows, is adjustable, works as follows. Part of the water vapor transporting exhaust gas flow enters the bypass line 12 while only the remaining part in the humidifier 7 arrives. This is the simplest means the supply of water vapor in the humidifier 7 vary, so that the gas stream to be humidified can only absorb the available water vapor and thus the dew point can be adjusted in the gas stream to be humidified by the supply of water vapor. This variant has the disadvantage that a part of the moist exhaust gas in the fuel cell system 1 according to 1 unused from the fuel cell system 1 escapes and thus also unused water reaches the environment. However, this may be due to a build up, as in 8th described below, be avoided.

The alternative or possibly additionally usable variant with the bypass line 13 provides that only part of the gas flow to be humidified by the humidifier 7 flows. This can then after the humidifier 7 again with the through the bypass line 13 flowing and thus dry gas stream ver be mixed. By a corresponding adjustment of the volume ratio through the bypass line 13 on the one hand and the humidifier 7 On the other hand, the dew point in the gas stream, which in the embodiment shown here then in the cathode compartment 5 occurs, varies or be adjusted.

In 2 is now a concrete embodiment of the humidifier 7 shown in cross section. On the representation of a device for varying the volume flows through the region of the membrane 8th on the one hand and the area of the bypass line 12 . 13 On the other hand, it has been omitted here. However, such a device is available.

The bypass line 12 . 13 (it does not matter for the operation, which is formed of the bypass lines in the manner shown here) is in the humidifier 7 integrated. This is particularly favorable when the membrane 8th is formed as a bundle of hollow fibers, since then the bypass line 12 . 13 can be easily integrated as a pipe in the bundle. However, there are also all other variants of membranes 8th conceivable. Also the geometric shape of the humidifier 7 and / or the bypass line 12 . 13 can be varied almost arbitrarily.

The one of the gas streams then flows from the inlet area 14 the humidifier 7 to the exit area 15 the same. The other flows through further line elements 16 , which are only indicated here in principle, in the area of the membranes 8th , Now sets a higher flow pressure loss for the of the inlet area 14 to the exit area 15 flowing gas stream in the region of the membrane 8th as in the area of the bypass line 12 . 13 advance, so the gas flow is predominantly through the area of the bypass line 12 . 13 stream. Due to the large surfaces of the membranes 8th this is generally always the case.

In order to achieve a control / regulation of the volume flows, the cross section of the bypass line 12 . 13 changed by a device for varying the volume flow. In 3 this device is as a valve lifter 17 shown. By a movement in the axial direction of the remaining inflow or Ausströmquerschnitt (The flow direction does not matter for the operation) in or out of the bypass line 12 . 13 be varied steplessly between "closed" and "open". The then no longer through the bypass line 12 . 13 flowing remaining part of the volume flow then flows through the region of the membranes 8th and is moistened there or gives off the water vapor contained in it.

In 4 another device is shown in an alternative embodiment. This is for a round or tubular design of the humidifier 7 suitable. The two discs shown 18 with their openings 19 be in the entrance or exit area 14 . 15 concentrically arranged in the flow direction immediately after one another. If you are now twisted against each other, so enter through the differently overlapping openings 19 different areas of the membranes 8th and / or the bypass line 12 . 13 free for flow.

In 5 is shown a further possibility of a device in which the variation of the cross-section through a flow on the disc 18 eccentrically mounted aperture plate 20 takes place, which can be brought into the region of the flow-through cross-section. For variation of the flow-through cross section in the region of the membranes 8th , here again a second disc in the sense of 4 Find use.

Next These devices shown here for varying the flow-through cross-section can also all other variants, combinations of conceivable and suitable Device are used, in particular screens and the like, which can be varied axially and / or in their diameter. Of the special advantage of the compact design opens up with all embodiments, which are designed so that an integration in the entry or exit area possible becomes.

In 6 is another embodiment of the humidifier 7 shown. Notwithstanding the in 2 illustrated embodiment, the bypass line 12 . 13 arranged eccentrically here. Will the bypass line 12 . 13 now opposite to the rest of the humidifier 7 arranged in the direction of gravity down, it may be in the area of the humidifier collecting possibly auskondensierendes water through the bypass line 12 . 13 ideally cited. The water can then pass through the bypass line 12 . 13 itself or through an optional drain opening 21 removed and made available to the system again, analogous to that in the liquid separator 11 accumulating water.

7 shows an alternative variant of the fuel cell system 1 , here comparable components with the analogous reference numerals as in 1 are provided. The gas generating device 6 is in the embodiment of the fuel cell system shown here 1 while a necessary device and not, as in the embodiment shown above, to be seen as an option. In the fuel cell system 1 in the embodiment play according to 7 is exclusively the bypass line 13 to set the dew point in the gas stream to be humidified, this works according to the principle already described above. In addition, this will be in the liquid separator 11 in liquid form separated water via a pipe 21 again the gas generating device 6 fed.

In the gas generating facility 6 This water is used together with a hydrocarbon-containing compound, for example, gasoline, diesel, alcohol or the like, in a conventional manner to a hydrogen-rich gas for operating the fuel cell 2 implemented. In addition to the water flowing through the pipe 22 the gas generating device 6 is supplied to the hydrocarbonaceous compound, the supply of which is not shown here, the gas generating means 6 an oxygen-containing medium supplied, which via a conveyor 23 through another humidifier 24 to the gas generating device 6 is encouraged. Also this other humidifier 23 is in principle analogous to the humidifier 7 built up. It also has comparable membranes 8th on, which are only permeable to water vapor. The humidity for humidifying the supply air to the gas generating device 6 also comes from the exhaust stream, which after the humidifier 7 still contains some residual moisture, which he in the further humidifier 24 to the supply air to the gas generating system 6 emits. In this construction, by through the bypass line 13 Furthermore given possibility of setting the dew point in the supply air to the cathode compartment 5 the ideal utilization of the moisture contained in the exhaust stream can be ensured. A variation of the dew point is in the supply air to the gas generator 6 not necessary, since here by the regulated supply of liquid water required for the ideal conversion of the starting materials water content is set anyway subsequently and the proportion of water vapor in the humidified supply air provides only a relatively small part of the required water.

In 8th a further embodiment is shown, wherein also here the reference numerals of comparable functioning components were selected analogous to the preceding figures.

This in 8th illustrated fuel cell system 1 has to set the dew point in the cathode compartment 5 supplied supply air flow the above-described variant using the bypass line 12 on. As already mentioned above, this variant has the fundamental disadvantage that a part of the moist exhaust gas around the humidifier 7 flows and the moisture contained in it is lost in principle. In the embodiment according to 8th This disadvantage is now avoided so that the proportion of the exhaust gas flow, which through the bypass line 12 flows, not directly with the exhaust gas flow to the humidifier 7 is mixed, but that in between the other humidifier 24 is arranged. The in the exhaust gas flow, which through the bypass line 12 flows, moisture contained can thus in the other humidifier 24 , analogous to 7 , in the supply air for the gas generating device 6 be transmitted. Analogous to 7 is here again a conveyor 23 shown, which for the promotion of supply air to the gas generating device 6 is needed. The fuel cell system 1 according to 8th now has another optional conveyor 25 on. This is necessary or may be necessary if in the Gaserzeugungseinrich device 6 a significantly higher pressure is present than in the area of the further humidifier device 24 , In this case, the conveyor would be 23 as a low-pressure compressor and the conveyor 25 Accordingly, designed as a high-pressure compressor to that for the gas generating device 6 If necessary, ensure necessary system pressure.

Also in the embodiment shown here, the approximately largest part of the moisture is used in the exhaust gas stream to moisten the corresponding gas streams to be humidified and or that for the gas generating device 6 provide needed water.

In addition to the embodiments shown here discretely, of course, all conceivable and useful combinations thereof as well as the use of a gas generating device 6 or conceivable with hydrogen stored in corresponding storage devices. For all fuel cell systems 1 It is true that with the water vapor present in the exhaust gas an ideal humidification of gas streams to be humidified, and here in particular of the supply air to the cathode compartment 5 , Can be ensured, the dew point can be set freely in this gas stream. The embodiments of the 7 and 8th moreover show possibilities for also recovering the residual moisture remaining in the exhaust gas flow, for example for operating the gas generating device 6 , if available.

Due to the particularly compact and robust design, the device for humidifying are particularly suitable for fuel cell systems 1 in vehicles on land, water and in the air, and this for both fuel cell systems 1 , which provide energy for driving purposes, in particular for fuel cell used as auxiliary power unit (APU / Auxiliary Power Unit) cell systems 1 ,

Claims (19)

Device for moistening at least one gas stream flowing to a fuel cell system, said gas stream flowing through a moistening device, through which also flows a moist gas stream, in particular a moist exhaust gas stream from the fuel cell system, and wherein the two gas streams through one or more water vapor permeable membrane ( ) Are separated from each other, characterized in that at least one bypass line ( 12 . 13 ) is provided, through which at least one of the gas streams is partially guided so that it does not interfere with the membrane ( 8th ) comes into contact. Apparatus according to claim 1, characterized in that a part of the gas stream to be humidified in the bypass line ( 13 ), wherein this part of the gas stream to be humidified after the bypass line ( 13 ) again with the humidifier ( 7 ) is merged by flowing part of the gas stream to be humidified. Apparatus according to claim 1 or 2, characterized in that a part of the moist exhaust gas flow in the bypass line ( 12 ) is guided. Apparatus according to claim 1, 2 or 3, characterized in that the gas stream to be humidified, the supply air to a cathode space ( 5 ) a fuel cell ( 2 ) of a fuel cell system ( 1 ). Device according to one of claims 1 to 4, characterized in that the gas stream to be humidified at least a portion of the exhaust gases from a fuel cell ( 2 ) of a fuel cell system ( 1 ) contains. Device according to one of claims 1 to 5, characterized in that the at least one bypass line ( 12 . 13 ) into the humidifier device ( 7 ) itself is integrated. Apparatus according to claim 6, characterized in that the at least one bypass line ( 12 . 13 ) in the humidifier device ( 7 ) is arranged so that optionally collecting condensate through the bypass line ( 12 . 13 ) drains off. Apparatus according to claim 6 or 7, characterized in that a device for varying the volume flow through the at least one bypass line ( 12 . 13 ) also in the humidifier device ( 7 ) is integrated. Apparatus according to claim 8, characterized in that the means for varying the volume flow through the at least one bypass line ( 12 . 13 ) in the manner of a valve tappet ( 17 ) is formed, which depending on the distance to an inlet or outlet opening of the bypass line ( 12 . 13 ) a different cross section of the bypass line ( 12 . 13 ) releases. Apparatus according to claim 8, characterized in that the means for varying the volume flow through the at least one bypass line ( 12 . 13 ) is designed in the manner of a variable diaphragm, which depending on the position and opening diameter a different cross section of the bypass line ( 12 . 13 ) releases. Apparatus according to claim 8, characterized in that the means for varying the volume flow through the at least one bypass line ( 12 . 13 ) in the manner of two rotatable with openings ( 19 ) provided discs ( 18 ) is formed, which depending on the angle of rotation to each other a different cross-section of the bypass line ( 12 . 13 ) and / or the area with the membrane ( 8th ). Device according to one of claims 1 to 11, characterized in that the moist gas stream after flowing through the humidifier ( 7 ) and / or the bypass line ( 12 ) in another similarly constructed humidifier ( 24 ) is performed to moisten a further to be moistened gas stream. Apparatus according to claim 12, characterized in that the further gas stream to be humidified, the supply air into a gas generating device ( 6 ) of the fuel cell system ( 1 ). A method for moistening a gas stream with a device for moistening at least to a fuel cell system flowing gas stream, said gas stream flows through a moistening device through which also a moist gas stream, in particular a moist exhaust gas stream from the fuel cell system flows, and wherein the two gas streams through a or a plurality of water vapor permeable membrane (s) are separated from each other, characterized in that at least one of the gas streams partially through at least one bypass line ( 12 . 13 ) so that it does not interfere with the membrane ( 8th ) comes into contact, wherein for setting a predetermined dew point in the at least one gas stream to be humidified, the amount of at least by the bypass line ( 12 . 13 ) to be humidified gas and / or humid gas is varied accordingly. Use of the device according to one of Claims 1 to 13 for drying a wet gas stream. Use of the device according to one of claims 1 to 13 for humidifying and / or drying a gas stream in a fuel cell system, together with the method of claim 14. Use according to claim 16, wherein the fuel cell system ( 1 ) is used as an electric power generator in a vehicle on land, sea or in the air. Use according to claim 17, wherein the electrical Energy generator is used to provide drive energy. Use according to claim 17 or 18, wherein the electrical Energy producer is used as auxiliary power generator (APU).